1. Field of the Invention
The present invention relates to a cooperative control apparatus adapted to effect cooperative control of an automatic transmission incorporating a frictional coupling device which is engaged during power driving of the vehicle and released during coasting of the vehicle, and an engine which generates a power to drive the vehicle through the automatic transmission.
2. Discussion of the Related Art
There is known an automotive vehicle having an automatic transmission equipped with a frictional coupling device such as a one-way clutch, which is placed in its engaged state during power driving of the vehicle with an engine power and is placed in its released state during coasting of the vehicle so as to inhibit engine braking while a shift lever is placed in a drive position xe2x80x9cDxe2x80x9d, for instance. An example of such a vehicle is disclosed in JP-A-3-117763.
In an automotive vehicle having an automatic transmission equipped with a frictional coupling device as described above, there arises a large difference between the input speed of the automatic transmission and the synchronizing speed (which is the output speed multiplied by the currently established speed ratio of the automatic transmission), immediately after a shift-down action of the automatic transmission which takes place due to a drop of the running speed of the vehicle during a coasting run as a result of a releasing operation of the accelerator pedal toward its non-operated or engine-idling position. The large speed difference indicated above requires a relatively long time for the input speed of the automatic transmission to rise to the synchronizing speed when the accelerator pedal is again depressed to accelerate the vehicle. Accordingly, the frictional coupling device requires a long response time, namely, it takes a long time for the frictional coupling device to be engaged to transmit the engine power to the vehicle drive wheels, unfavorably resulting in deteriorated drivability of the vehicle as felt by the vehicle operator.
It is therefore an object of the present invention to provide a cooperative control apparatus for controlling an automatic transmission and an engine of an automotive vehicle, which apparatus permits the engine power to be transmitted to the vehicle drive wheels in a relatively short time after an operation of the accelerator pedal to accelerate vehicle following a coasting run of the vehicle.
The above object may be achieved according to the principle of the present invention, which provides a cooperative control apparatus for controlling an automotive vehicle, so as to effect a cooperative control of an automatic transmission and a drive power source which produces an output to drive the vehicle through the automatic transmission, the automatic transmission incorporating a frictional coupling device which is engaged to place the automatic transmission in a power transmitting state, during power driving of the vehicle with the output of the drive power source, and is released to place the automatic transmission in a power disconnecting state, during coasting of the vehicle, the cooperative control apparatus comprising: control initiating condition determining means for determining whether a control initiating condition required to initiate an output increase control for temporarily increasing the output of the drive power source is satisfied or not, depending upon whether an operation to accelerate the vehicle is performed during the coasting of the vehicle while the frictional coupling device is placed in a released state; and output increase control means operable when the control initiating condition determining means determines that the control initiating condition is satisfied, for effecting the output increase control such that the output of the drive power source is larger by a predetermined amount than when the output increase control is not effected.
In the cooperative control apparatus of the present invention constructed as described above, the output of the drive power source is made larger by the predetermined amount by the output increase control means when the control initiating determining means determines that the control initiating condition is satisfied, upon an operation to accelerate the vehicle during coasting of the vehicle with the frictional coupling device placed in the released state, than when the control initiating determining means does not determine that the control initiating condition is satisfied. The output increase control is effective to reduce the time required for the input shaft speed of the automatic transmission to be raised to the synchronizing speed which is a product of the output shaft speed and the speed ratio of the currently established forward drive position of the automatic transmission during the vehicle coasting. Accordingly, the output increase control reduces the accelerating response time from the moment of the vehicle accelerating operation to the moment of engagement of the frictional coupling device to enable the automatic transmission to transmit the vehicle drive power, so that the drivability of the vehicle as felt by the vehicle operator is improved.
In one preferred form of this invention, the frictional coupling device is a one-way clutch which is placed in an engaged state during the power driving of the vehicle, and is placed in the released state when an input shaft speed of the automatic transmission is lower than a synchronizing speed which is a product of an output shaft speed of the automatic transmission and a speed ratio of a currently established forward drive position of the automatic transmission. This one-way clutch is mechanically constructed such that the one-way clutch is automatically engaged when a power is transmitted from the drive power source to drive wheels of the automotive vehicle, and is automatically released when a power is transmitted in the reverse direction. In this form of the invention, the one-way clutch need not be electrically controlled to place this one-way clutch in the released state.
In another preferred form of this invention, the output increase control means increases the output of the drive power source such that an input shaft speed of the automatic transmission in the process of increase of the output of the drive power source does not exceed a synchronizing speed which is a product of an output shaft speed of the automatic transmission and a speed ratio of a currently established forward drive position of the automatic transmission. This form of the invention does not suffer from a rapid reduction in the rate of increase of the input shaft speed of the automatic transmission upon engagement of the frictional coupling device, so that an otherwise possible engaging shock of the frictional coupling device can be suitably avoided.
In a further preferred form of this invention, the output increase control means increases the output of the drive power source such that the output is kept increased while an input shaft speed of the automatic transmission is not higher than a synchronizing speed which is a product of an output shaft speed of the automatic transmission and a speed ratio of a currently established forward drive position of the automatic transmission. In this form of the invention, the input shaft speed of the automatic transmission can be rapidly raised to a value close to the synchronizing speed, whereby the accelerating response of the vehicle can suitably be improved.
In a yet further preferred form of this invention, the control initiating condition determining means includes input shaft speed determining means for determining whether an input shaft speed of the automatic transmission is lower than a synchronizing speed minus a predetermined first value, the synchronizing speed being a product of an output shaft speed of the automatic transmission and a speed ratio of a currently established forward drive position of the automatic transmission. The output increase control means continues to increase the output of the drive power source while the input shaft speed determining means determines that the input shaft speed is lower than the synchronizing speed minus the predetermined first value. In this form of the invention, the control initiating condition determining means does not determine that the control initiating condition is satisfied, when the input shaft speed is not lower than the synchronizing speed minus the predetermined first value. This form of the invention is effective to avoid an unnecessary operation to increase the output of the drive power source, and assure the initiation of the output increase control of the drive power source immediately before the input shaft speed of the automatic transmission has reached the synchronizing speed, so that an engaging shock of the automatic transmission can be suitably prevented.
In a still further preferred form of this invention, the control initiating condition determining means includes includes shift-down completion determining means for determining whether a shift-down action of the automatic transmission which has been initiated before the operation to accelerate the vehicle during the coasting of the vehicle has been substantially completed. The control initiating condition determining means determines that the control initiating condition is satisfied, when the shift-down completion determining means determines that the shift-down action has been substantially completed. In this form of the invention, the initiation of the output increase control of the drive power source can be avoided when the frictional coupling device which should be engaged to complete the shift-down action is still partially released or or slipping.
In another preferred embodiment of this invention, the control initiating condition determining means includes pre-shift-up-initiation determining means for determining whether a frictional coupling device which should be engaged to effect a shift-up action of the automatic transmission following a shift-down action of the automatic transmission which has been commanded before the operation to accelerate the vehicle during the coasting of the vehicle has not been substantially engaged. The control initiating condition determining means determines that the control initiating condition is satisfied, when the pre-shift-up-initiation determining means determines that the frictional coupling device which should be engaged to effect the shift-up action has not been substantially engaged. In this form of the invention, the output increase control of the drive power source is effected even after the generation of a command to shift up the automatic transmission, until the frictional coupling coupling device which should be engaged to effect the shift-up action has been substantially engaged.
In a further preferred form of this invention, the control initiating condition determining means includes vehicle acceleration determining means for determining whether an acceleration value of the vehicle is lower than a predetermined lower limit, and determines that the control initiating condition is satisfied, when the vehicle acceleration determining means determines that the acceleration value of the vehicle is lower than the predetermined lower limit. This form of the invention is effective to prevent the output increase control of the drive power source after the vehicle has been sufficiently accelerated, for some reason or other.
In a still further preferred form of this invention, the cooperative control apparatus further comprises control terminating condition determining means for determining whether a control terminating condition required to terminate the output increase control of the output of the drive power source is satisfied, the control terminating condition determining means including at least one of (a) time lapse monitoring means for determining whether a time lapse after a moment of initiation of an increase of the output of the drive power source has exceeded a predetermined maximum increase period, (b) input shaft speed determining means for determining whether an input shaft speed of the automatic transmission has been raised above a synchronizing speed minus a predetermined second value, the synchronizing speed being a product of an output shaft speed of the automatic transmission and a speed ration of a currently established forward drive position of the automatic transmission, and (c) accelerator non-operation detecting means for determining whether an accelerator pedal which has been depressed to perform the operation to accelerate the vehicle during the coasting of the vehicle has been returned to a non-operated position thereof, the control terminating means determining that the control terminating condition is satisfied, when at least one of the time lapse monitoring means, the input shaft speed determining means and the accelerator non-operation detecting means obtains an affirmative decision, the output increase control means continuing the output increase control of the output of the drive power source until the control terminating condition determining means determines that the control terminating condition is satisfied. In this form of the invention, the output increase control of the drive power source is restricted in terms of the time period of the output increase and the input shaft speed of the automatic transmission, and is prevented when the vehicle operator does not have an intention to accelerate the vehicle during its coasting run.
In a yet further preferred form of this invention, the output increase control means increases the output of the drive power source by an amount up to a predetermined maximum amount at a predetermined rate, hold the output at the increased value for a period of time which is a difference of a predetermined maximum period of increase of the output minus a period of time for which the output has been increased by the predetermined maximum amount, and then reduce the output at a predetermined rate. This form of the invention is effective to avoid an abrupt increase or decrease in the intake air quantity of the drive power source, thereby preventing an increase in the concentration of noxious gases in the exhaust emission. This arrangement is particularly effective where the drive power source is an engine having a relatively large displacement, and a high tendency of air intake delay.
In a still another preferred form of this invention, the output increase control means includes increase amount determining means for determining a maximum amount of increase of the output of the drive power source depending upon a difference between a synchronizing speed and an input shaft speed of the automatic transmission, the synchronizing speed being equal to a product of an output shaft speed of the automatic transmission and a speed ratio of a currently established forward drive position of the automatic transmission, the output increase control means increasing the output of the drive power source by an amount up to the maximum amount determined by the increase amount determining means. In this form of the invention, the output of the drive power source is increased by an amount up to the determined maximum amount determined by the increase amount determining means. Accordingly, the output of the drive power source is increased by an appropriate amount corresponding to the above-indicated difference, to assure a sufficiently high degree of accelerating response of the vehicle while avoiding a shock of the automatic transmission upon engagement of the frictional coupling device.